The most common thermal pack is a rubberized container for holding hot water or ice. The hot-water bottle or ice bag, as the case may be, is applied to afflicted body parts to apply heat or cold, as prescribed. Traditionally, the hot water bottle or ice bag is a rubber or rubber-like bladder which sheds water and dry heat transfer is accomplished. When moist heat or moist coolness is required, a moist towel is wrapped around the bladder. The towel provides the moist heat transfer but also reduces the efficiency of the heat transfer.
In recent years, the devices have been modified by the use of a rubberized fabric which has limited moisture retention properties and enables the utilization of moist heat transfer for a limited period, for example until the moisture in the fabric evaporates. The moisture-retention ability of the fabric is limited since the fabric must be impermeable to avoid leaking, and the moisture is retained on the outer surface of the fabric primarily by capillary attraction or by wicking.